The research proposal will investigate the mechanisms governing the regulation of expression of mouse heavy chain immunoglobulin (Ig) genes at the DNA and RNA levels in plasmacytomas and hybridoma cell lines using recombinant DNA techniques. cDNA copies of heavy chain Ig mRNAs specifying a variety of constant regions gamma 2b, gamma 2a, alpha and mu will be cloned into plasmids. The recombinant DNAs will be conclusively identified by their ability to specifically arrest the in vitro cell-free translation of the appropriate Ig mRNA. The cloned Ig cDNAS will be used as probes for the isolation of their genomic sequences from "shot-gun libraries" prepared from both germ line and plasmacytoma DNA. The structural features of the cDNA clones will be compared to their genomic counterparts by heteroduplex mapping and rapid DNA sequencing techniques. These Ig and genomic clones will be used in a variety of studies designed to improve our understanding of Ig gene function and regulation: (a) To explore the nature of potential alterations in the organization of Ig genes during plasma cell differentiation, (b) The molecular basis of the heavy chain constant region switch, (c) The molecular basis of allelic exclusion, (d) The mechanism(s) of diversification of VH genes of knowm antigen specificity, (e) The nature of hidden allotypes, (f) Structural and metabolic features of the initial transcription units of Ig genes.